U.S. patent application number 11/606190 was filed with the patent office on 2007-06-07 for process of producing high-yield pulp.
This patent application is currently assigned to Akzo Nobel N.V.. Invention is credited to Magnus Lars Paulsson, Eva Linnea Elisabeth Wackerberg, Karin Susanne Maria Walter.
Application Number | 20070125507 11/606190 |
Document ID | / |
Family ID | 38117559 |
Filed Date | 2007-06-07 |
United States Patent
Application |
20070125507 |
Kind Code |
A1 |
Walter; Karin Susanne Maria ;
et al. |
June 7, 2007 |
Process of producing high-yield pulp
Abstract
The present invention relates to a process for preparing a
high-yield pulp comprising a) treating a lignocellulose containing
material chemically by means of an oxidising system comprising at
least one non-enzymatic oxidant substantially free from ozone and
chlorine dioxide and an activator at a pH from about 2 to about
6.5; and b) treating the lignocellulose containing material
mechanically for a time sufficient to produce a high-yield pulp,
wherein the lignocellulose containing material is chemically
treated prior to and/or during any mechanical treatment stage, and
wherein the lignocellulose containing material is not chemically
treated at a pH from about 11.5 to about 14 between stages a) and
b).
Inventors: |
Walter; Karin Susanne Maria;
(Goteborg, SE) ; Wackerberg; Eva Linnea Elisabeth;
(Goteborg, SE) ; Paulsson; Magnus Lars; (Goteborg,
SE) |
Correspondence
Address: |
AKZO NOBEL INC.
INTELLECTUAL PROPERTY DEPARTMENT
120 WHITE PLAINS ROAD 3RD FLOOR
TARRTOWN
NY
10591
US
|
Assignee: |
Akzo Nobel N.V.
Arnhem
NL
6824 BM
|
Family ID: |
38117559 |
Appl. No.: |
11/606190 |
Filed: |
November 29, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60742032 |
Dec 2, 2005 |
|
|
|
Current U.S.
Class: |
162/24 ; 162/26;
162/65; 162/70; 162/78; 162/81 |
Current CPC
Class: |
D21C 9/10 20130101; D21C
1/08 20130101; D21B 1/16 20130101 |
Class at
Publication: |
162/024 ;
162/026; 162/070; 162/078; 162/081; 162/065 |
International
Class: |
D21C 1/02 20060101
D21C001/02; D21B 1/16 20060101 D21B001/16 |
Claims
1. A process for preparing a high-yield pulp comprising a) treating
a lignocellulose containing material chemically by means of an
oxidising system comprising at least one non-enzymatic oxidant
substantially free from ozone and chlorine dioxide and an activator
at a pH from about 2 to about 6.5; and b) treating the
lignocellulose containing material mechanically for a time
sufficient to produce a high-yield pulp, wherein the lignocellulose
containing material is chemically treated prior to and/or during
any mechanical treatment stage, and wherein the lignocellulose
containing material is not chemically treated at a pH from about
11.5 to about 14 between stages a) and b).
2. A process according to claim 1, wherein the pH is from about 2.5
to about 6.
3. A process according to claim 1, wherein the pH is from about 3
to about 5.5.
4. A process according to claim 1 wherein the high-yield pulp is
mechanical pulp, refiner mechanical pulp, groundwood pulp,
chemimechanical pulp, semichemical pulp, thermomechanical and/or
chemithermomechanical pulp.
5. A process according to claim 1, wherein said lignocellulose
containing material comprises non-defibrated wood.
6. A process according to claim 1, wherein the lignocellulose
containing material comprises mechanically treated lignocellulose
containing material.
7. A process according to claim 1, wherein the oxidising system is
applied between two mechanical treatment stages.
8. A process according to claim 1, wherein the lignocellulose
containing material comprises softwood and/or hardwood.
9. A process according to claim 1, wherein the lignocellulose
containing material comprises softwood.
10. A process according to claim 1, wherein the non-enzymatic
oxidant is selected from peroxy compounds, halogen containing
oxidants, oxygen, nitrogen oxides, and combinations thereof.
11. A process according to claim 1, wherein the non-enzymatic
oxidant is selected from peroxy compounds.
12. A process according claim 1, wherein the non-enzymatic oxidant
is hydrogen peroxide.
13. A process according to claim 1, wherein the oxidising system
comprises an activator selected from metal ions, TAED, cyanamide,
or combinations thereof.
14. A process according to claim 1, wherein the oxidising system
comprises an activator selected from transition metal ions.
15. A process according to claim 1, wherein the oxidising system
further comprises an enhancer selected from nitrogen-containing
polycarboxylic acids, nitrogen-containing polyphosphonic acids,
nitrogen-containing polyalcohols, oxalic acid, oxalate, glycolate,
ascorbic acid, citric acid, nitrilo acetate, gallic acid, fulvic
acid, itaconic acid, haemoglobin, hydroxybenzenes, catecholates,
quinolines, dimethoxybenzoic acids, dihydroxybenzoic acids,
dimethoxybenzylalcohols, pyridine, histidylglycine, phthalocyanine,
acetonitril, 18-crown-6 ether, mercaptosuccinic acid,
cyclohexadienes, polyoxomethalates, and combinations thereof.
16. A process according claim 1 wherein the oxidising system
further comprises an enhancer selected from EDTA, DTPA, NTA, and
combinations thereof.
17. A process for preparing a high-yield pulp comprising a)
treating a lignocellulose containing material chemically by means
of an oxidising system comprising at least one non-enzymatic
oxidant substantially free from ozone and chlorine dioxide and an
activator at a pH from about 2 to about 6.5; and b) treating the
lignocellulose containing material mechanically for a time
sufficient to produce a high-yield pulp, wherein the lignocellulose
containing material is chemically treated prior to and/or during
any mechanical treatment stage, and wherein the lignocellulose
containing material is not chemically treated at a pH from about
11.5 to about 14 between stages a) and b), wherein the activator is
selected from transition metal ions.
18. A process for preparing a high-yield pulp comprising a)
treating a lignocellulose containing material chemically by means
of an oxidising system comprising at least one non-enzymatic
oxidant comprising hydrogen peroxide and being substantially free
from ozone and chlorine dioxide and an activator at a pH from about
2 to about 6.5; and b) treating the lignocellulose containing
material mechanically for a time sufficient to produce a high-yield
pulp, wherein the lignocellulose containing material is chemically
treated prior to and/or during any mechanical treatment stage, and
wherein the lignocellulose containing material is not chemically
treated at a pH from about 11.5 to about 14 between stages a) and
b), wherein the activator is selected from transition metal ions.
Description
[0001] The present invention relates to a process for producing a
high-yield pulp from a lignocellulose containing material.
BACKGROUND OF THE INVENTION
[0002] Enhanced production and efficient utilization of
lignocellulosic products are issues of high importance to both the
pulp and paper industry and society. The production of mechanical
and chemimechanical pulps is an efficient way of using the world's
natural resources since the yield of these manufacturing processes
is high and the environmental impact is relatively low. Mechanical
and chemimechanical pulping constitute about 25% of the total
virgin fibre production in the world. One drawback with mechanical
pulping processes is the high energy consumption that represents
about 20% of the energy demand of papermaking in the world. The
energy alone represents 25-50% of the total manufacturing cost of a
thermomechanical pulp. (TMP) depending on where in the world the
mechanical pulp mill is located. In a TMP mill, about 80% of the
energy is consumed during mainline refining (primary, secondary
etc.), reject and low-consistency refining. The rest of the energy
is consumed in pumps, agitators, screens, blowers, fans and
mechanical drives. This means that most of the energy is used for
fibre separation and for developing the fibres to make them
suitable for the defined end-usage. It is therefore extremely
important to find suitable ways of reducing the consumption of
energy. However, a process that reduces the energy consumption
during production of mechanical pulp is of limited interest for
conventional products if the pulp or paper strength is, at the same
time, substantially reduced or if the environmental effect is
substantially impaired.
[0003] EP 494 519 A1 relates to a process comprising impregnating
chips with an alkaline peroxide solution containing stabilizers for
peroxide followed by mechanical defibration, in which the wood
chips are pre-treated prior to peroxide impregnation. However, the
process of EP 494 519 A1 involves extensive capital investment and
does not result in sufficient energy saving with maintained pulp
yield and pulp properties.
[0004] One object of the invention is to reduce the energy
consumption in a process which is simple to install in a high-yield
pulping process and without substantially reducing the fibre length
or strength properties of the produced pulp. A further object of
the present invention is to provide such a process while
maintaining the pulp yield at an acceptable level. A further
intention of the present invention is to provide a facilitated
process without need of considerable capital investments. A further
intention is to provide a process in the absence of alkaline
treatment stages while improving or at least not substantially
affecting properties of the obtained high-yield pulp, e.g. strength
properties.
THE INVENTION
[0005] The present invention relates to a process for preparing a
high-yield pulp comprising [0006] a) treating a lignocellulose
containing material chemically by means of an oxidising system
comprising at least one non-enzymatic oxidant substantially free
from ozone and chlorine dioxide and an activator at a pH from about
2 to about 6.5; and [0007] b) treating the lignocellulose
containing material mechanically for a time sufficient to produce a
high-yield pulp, wherein the lignocellulose containing material is
chemically treated prior to and/or during any mechanical treatment
stage, and wherein the lignocellulose containing material is not
chemically treated at a pH from about 11.5 to about 14 between
stages a) and b).
[0008] According to one embodiment, the pH is from about 2.5 to
about 6, for example from about 2.5 to about 5.5 or from about 3 to
about 5.5 such as from about 3 to about 4. According to one
embodiment, the pH is from about 3.5 to about 5.
[0009] According to one embodiment, the lignocellulose containing
material is not chemically treated between stages a) and b) at a pH
from about 7 to about 14, for example from about 8 to about 14 or
from about 9 to about 14, e.g. from about 10 to about 14 or from
about 10.5 to about 14 or from about 11 to about 14.
[0010] According to one embodiment, the lignocellulose containing
material is not chemically treated before stage a) at a pH from
about 7 to about 14, for example from about 8 to about 14 or from
about 9 to about 14, e.g. from about 10 to about 14 or from about
10.5 to about 14 or from about 11 to about 14 or from about 11.5 to
about 14.
[0011] The term high-yield pulp may comprise e.g. mechanical pulp
(MP), refiner mechanical pulp (RMP), pressurized refiner mechanical
pulp (PRMP), thermomechanical pulp (TMP), thermomechanical chemical
pulp (TMCP), high-temperature TMP (HT-TMP) RTS-TMP, Thermopulp,
groundwood pulp (GW), stone groundwood pulp (SGW), pressure
groundwood pulp (PGW), super pressure groundwood pulp (PGW-S),
thermo groundwood pulp (TGW), thermo stone groundwood pulp (TSGW),
chemimechanical pulp (CMP), chemirefinermechanical pulp (CRMP),
chemithermomechanical pulp (CTMP), high-temperature CTMP (HT-CTMP),
sulphite-modified thermomechanical pulp (SMTMP), reject CTMP
(CTMP.sub.R), groundwood CTMP (G-CTMP), semichemical pulp (SC),
neutral sulphite semi chemical pulp (NSSC), high-yield sulphite
pulp (HYS), biomechanical pulp (BRMP), pulps produced according to
the OPCO process, explosion pulping process, Bi-Vis process,
dilution water sulfonation process (DWS), sulfonated long fibres
process (SLF), chemically treated long fibres process (CTLF), long
fibre CMP process (LFCMP) or any modifications and combinations
thereof. According to one embodiment, the high-yield pulp has a
yield of at least about 60%, for example at least about 70%, or at
least about 80%, or at least about 85%. According to one
embodiment, the high-yield pulp has a yield of at least about 90%
such as at least about 95%. The pulp may be a bleached or
non-bleached pulp.
[0012] According to one embodiment, the lignocellulose containing
material comprises non-defibrated wood. According to one
embodiment, the lignocellulose containing material comprises
mechanically treated lignocellulose containing material. According
to one embodiment, the oxidising system is applied between two
mechanical treatment stages. The lignocellulose containing material
may comprise e.g. wood logs, finely-divided raw materials,
including woody materials, such as wood particles (e.g. in the form
of wood chips, wood shavings, wood fibres and saw dust) and fibres
of annual or perennial plants including non-wood. The woody raw
material can be derived from hardwood or softwood species, such as
birch, beech, aspen such as European aspen, alder, eucalyptus,
maple, acacia, mixed tropical hardwood, pine such as loblolly pine,
fir, hemlock, larch, spruce such as Black spruce or Norway spruce,
and mixtures thereof. Non-wood plant raw material can be provided
from e.g. straws of grain crops, reed canary grass, reeds, flax,
hemp, kenaf, jute, ramie, sisal, abaca, coir, bamboo, bagasse or
combinations thereof.
[0013] According to one embodiment, the oxidant is selected from
peroxy compounds, halogen containing oxidants, oxygen, nitrogen
oxides or combinations thereof. The oxidising system, including the
non-enzymatic oxidant, being substantially free from ozone can be
advantageous due to the fact that ozone does not provide a
sufficient pulp yield due to low selectivity and is usually a more
expensive alternative. By the term "substantially free from ozone"
is meant that the oxidising system comprises less than 5 wt %, for
example less than 2 wt % or less than 1 wt % ozone (calculated as
100%) based on the total weight of the oxidising system. By the
term "substantially free from chlorine dioxide" is meant that the
oxidising system comprises less than 5 wt %, or less than 2 wt % or
less than 1 wt % chlorine dioxide (calculated as 100%) based on the
total weight of oxidising system.
[0014] According to one embodiment, the non-enzymatic oxidant and
the activator can be added at any position prior to or during any
mechanical treatment stage. According to one embodiment, the
oxidising system is applied to the lignocellulose containing
material at one or several stages before or during mechanical
treatment. According to one embodiment, the oxidising system is
applied as an inter-stage treatment between two mechanical
treatment stages. According to one embodiment, the process uses two
or three mechanical treatment stages such as refining stages
between which treatment of the lignocellulose containing material
can be performed with the oxidising system. However, any other
number of stages may also be used including one or several reject
refining stages. According to one embodiment, the oxidising system
is applied to a reject refining stage.
[0015] The activator may be any suitable substance capable of
accelerating the oxidation in the presence of a non-enzymatic
oxidant. According to one embodiment, the activator is selected
from metal ions, TAED, cyanamide, cupper sulfate, iron sulfate, and
mixtures thereof. According to one embodiment, the activator is a
transition metal.
[0016] According to one embodiment, the oxidising system comprises
an enhancer that facilitates/controls the oxidation. According to
one embodiment, the enhancer is selected from nitrogen-containing
polycarboxylic acids, nitrogen-containing polyphosphonic acids,
nitrogen-containing polyalcohols, oxalic acid, oxalate, glycolate,
ascorbic acid, citric acid nitrilo acetate, gallic acid, fulvic
acid, itaconic acid, haemoglobin, hydroxybenzenes, catecholates,
quinolines, dimethoxybenzoic acids, dihydroxybenzoic acids,
dimethoxybenzylalcohols, pyridine, histidylglycine, phthalocyanine,
acetonitrile, 18-crown-6-ether, mercaptosuccinic acid,
cyclohexadienes, polyoxomethalates, and combinations thereof.
[0017] According to one embodiment, the enhancer is selected from
nitrogen-containing organic compounds, primarily
nitrogen-containing polycarboxylic acids, nitrogen-containing
polyphosphonic acids, nitrogen-containing polyalcohols, and
mixtures thereof. According to one embodiment, the enhancer is
selected from diethylenetriaminepentaacetic acid (DTPA),
ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid
(NTA), and combinations thereof. According to one embodiment, the
enhancer is selected from compounds based on other
aminopolycarboxylic acids, polyphosphates or polyphosphonic acids,
hydroxycarboxylates, hydrocarboxylic acids, dithiocarbamate, oxalic
acid, iminodisuccinic acid, [S,S']-etylenediaminedisuccinic acid,
glycolate, ascorbic acid, citric acid, nitrilo acetate, gallic
acid, fulvic acid, itaconic acid. According to one embodiment, the
enhancer is selected from oxalate, haemoglobin, dihydroxybenzene
(e.g. hydroquinone), trihydroxybenzene, catecholates (e.g.
4,5-dimethoxycatechol, 2,3 dihydroxy-benzene, 4-methyl catechol),
quinoline, hydroxyquinoline (e.g. 8-hydroxyquinoline),
dihydroxybenzoic acid (e.g. 3,4-dihydroxybenzoic acid,
2,3-dihydroxybenzoic acid), 3,4-dimethoxybenzylalcohol,
3,4-dimethoxybenzoic acid, 3,4-dimethoxy toluene, pyridine,
histidylglycine, phthalocyanine, acetonitril, 18-crown-6 ether,
mercaptosuccinic acid, 1,3-cyclohexadiene, polyoxomethalates.
According to one embodiment, the oxidising system comprises as an
enhancer also at least one enzyme.
[0018] According to one embodiment, the lignocellulose containing
material is treated with the oxidising system for from about one
second to about ten hours. According to one embodiment, the
lignocellulose containing material is treated with the oxidising
system for from about five seconds to about five hours. According
to one embodiment, the lignocellulose containing material is
treated with the oxidising system for from about ten seconds to
about three hours.
[0019] According to one embodiment, the lignocellulose containing
material is treated at a temperature from about 30 to about
200.degree. C. According to one embodiment, the lignocellulose
containing material is treated at a temperature from about 50 to
about 180.degree. C. According to one embodiment, the
lignocellulose containing material is treated at a temperature from
about 80 to about 180.degree. C.
[0020] According to one embodiment, the non-enzymatic oxidant
(calculated as 100%) is added in an amount from about 0.1 to about
5 wt % based on the weight of the lignocellulose containing
material. According to one embodiment, the non-enzymatic oxidant
(calculated as 100%) is added in an amount from about 0.2 to about
3 wt % based on the weight of the lignocellulose containing
material. According to one embodiment, the non-enzymatic oxidant
(calculated as 100%) is added in an amount from about 0.3% to about
2 wt % based on the weight of the lignocellulose containing
material.
[0021] According to one embodiment, an activator (calculated as
100%) is added in an amount from about 0.0001 to about 1 wt % based
on the weight of the lignocellulose containing material. According
to one embodiment, an activator (calculated as 100%) is added in an
amount from about 0.001 to about 0.5 wt % based on the weight of
the lignocellulose containing material. According to one
embodiment, an activator (calculated as 100%) is added in an amount
from about 0.0025 to about 0.1 wt % based on the weight of the
lignocellulose containing material. According to one embodiment, an
activator is added prior to or during any mechanical treatment
stage, either separately or simultaneously with a non-enzymatic
oxidant. The activator may thus be added either before,
simultaneously or after the addition of a non-enzymatic oxidant.
This may be just before the addition of a non-enzymatic oxidant
before a mechanical treatment stage such as a refiner, but may also
be before e.g. a primary refiner whereas the non-enzymatic oxidant
is added after the primary refiner but before a secondary
refiner.
[0022] According to one embodiment, an enhancer (calculated as
100%) is added in an amount from about 0.001 to about 1 wt % based
on the weight of lignocellulose containing material.
[0023] According to one embodiment, an enhancer (calculated as 100%
pure compound) is added in an amount from about 0.01 to about 0.5
wt % based on the weight of the lignocellulose containing material.
According to one embodiment, an enhancer (calculated as 100%) is
added in an amount from about 0.05 to about 0.3 wt % based on the
weight of the lignocellulose containing material. According to one
embodiment, an enhancer is added prior to or during any mechanical
treatment stage, either separately or simultaneously with a
non-enzymatic oxidant and optionally an activator. The enhancer may
thus be added either before, simultaneously or after the addition
of a non-enzymatic oxidant. This may be just before the addition of
the non-enzymatic oxidant before a mechanical treatment stage such
as a refiner, but may also be before e.g. a primary refiner whereas
the non-enzymatic oxidant is added after the primary refiner but
before a secondary refiner.
[0024] The mechanical treatment may be performed in one or several
stages. Typically, the mechanical treatment may be performed in two
stages or more including a reject mechanical treatment stage where
up to 60 wt % of the lignocellulose containing material may be
passed through. The mechanical treatment stages usually are
performed by passing the lignocellulose containing material through
grinders, and/or refiners. However, other mechanical treatments may
also be performed in equipments as, e.g. plug screws (e.g.
impressafiner), roller mills (e.g. Szego mill), double shaft
extruders (Bi-Vis screw extruder), the reciprocating apparatus, RT
Fiberizerr.TM., dispersers or in any combinations thereof.
[0025] According to one embodiment, the non-enzymatic oxidant is
selected from inorganic peroxy compounds such as hydrogen peroxide
or hydrogen peroxide generating compounds such as salts of
percarbonate, perborate, peroxysulfate, peroxyphosphate,
peroxysilicate or corresponding weak acids.
[0026] According to one embodiment, the non-enzymatic oxidant is
selected from organic peroxy compounds such as peroxy carboxylic
acids, e.g. peracetic acid and perbenzoic acid.
[0027] According to one embodiment, the oxidising system comprises
halogen containing oxidants such as chlorite, hypochlorite, chloro
sodium salt of cyanuric acid. According to one embodiment, the
oxidising system comprises oxygen and/or nitrogen oxides such as NO
or NO.sub.2. According to one embodiment, the oxidizing system
comprises combinations of different oxidants, which can be either
added or re-used from the process steps which generate the
non-enzymatic oxidants.
[0028] According to one embodiment, the oxidising system further
comprises activators such as metal ions, e.g. Fe, Mn, Co, Cu, W or
Mo, or TAED, cyanamide or combinations thereof. According to one
embodiment, metal ions such as transistion metal ions may be used
in the form of acids or salts or complexes with common organic or
inorganic compounds.
[0029] According to one embodiment, ultraviolet radiation or other
radiation is applied to the non-enzymatic oxidant or to the
lignocellulose containing material being treated with the
non-enzymatic oxidant, optionally in combination with an
enhancer.
[0030] According to one embodiment, enhancers, e.g. complexing
agents, chelating agents or ligands are comprised in the oxidising
system. These enhancers may facilitate/control the oxidising effect
depending on the amount thereof being added.
[0031] According to one embodiment, both an enhancer and an
activator are comprised in the oxidising system.
[0032] The following examples will illustrate how the described
invention may be performed without limiting the scope of it.
[0033] All parts and percentages refer to part and percent by bone
dry weight, if not otherwise stated. The chemicals are calculated
as 100%.
EXAMPLE 1
[0034] Black spruce (Picea mariana) wood was used for the
production of thermomechanical pulp (TMP). The wood logs were
debarked and chipped and washed prior to preheating (4.14 bar
steaming pressure, 40 s retention time) and refining operations. A
three-stage refining setup was used and the energy input was varied
in the last refining stage to obtain pulps with different freeness
(refining) levels. A single disc 36'' pressurized refiner (model
36-1CP run at 1800 rpm) was used in the first refining stage and a
double disc 36'' atmospheric refiner (model 401, 1200 rpm) in the
second and third stages. The energy input in the primary refiner
was about 500 kWh/bone dry metric ton (bdmt) and in the second
refining stage approximately 1000 kWh/bdmt. In most cases, three
tertiary refining stages with a targeted energy input of 400, 800
and 1200 kWh/bdmt were performed. All trials were run at constant
conditions which mean that the variation in specific energy
consumption and pulp and paper properties is a result of the
chemicals added during the trials. The energy consumption measured
in the pilot plant for the references (TMP.sub.Ref, and
TMP.sub.Ref, see tables and figures below) is comparable to
commercial operation.
[0035] Each refining series described in the following examples was
produced according to the procedure described above.
[0036] A TMP reference (TMP.sub.Ref1 in figures and tables below)
was produced without addition of chemicals. The degree of refining
(freeness) as a function of the specific energy consumption (SEC)
can be seen in FIG. 1 and the strength of the resulting pulp in
Tables 1 and 2. FIG. 2 shows the fibre length distribution and FIG.
3 the fibre width distribution of the resulting pulp (freeness of
approximately 100 ml CSF).
[0037] A TMP reference produced under more acidic conditions
(denoted TMP.sub.Ref2) was also provided to make sure that the
energy reduction obtained is a consequence of the method described
in the present invention and not an effect of lowering the pH
during refining. The pH was lowered by adding 0.19 wt % sulphuric
acid (H.sub.2SO.sub.4) based on the weight of bone dry wood to the
refiner eye (inlet) of the primary refiner. The pH of the resulting
pulp was 3.8. The TMP properties of the produced pulp can be found
in FIGS. 1-3 and Tables 1-2 below.
[0038] A TMP manufactured according to the present invention using
acid hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.08
wt % iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight
of bone dry wood to the refiner eye of the primary refiner and 1.0
wt % hydrogen peroxide (H.sub.2O.sub.2) based on the weight of bone
dry wood to the blow line of the primary refiner. The pH of the
resulting pulp was 3.6. The pulp is denoted TMP.sub.HP1Fe in
figures and tables below.
[0039] A second TMP manufactured according to the present invention
using acid hydrogen peroxide (H.sub.2O.sub.2) was produced by
adding 0.15 wt % (of bone dry wood) iron sulfate
(FeSO.sub.4.times.7 H.sub.2O) to the refiner eye of the primary
refiner and 1.1 wt % (of bone dry wood) hydrogen peroxide
(H.sub.2O.sub.2) to the blow line of the primary refiner. The pH of
the resulting pulp was 3.4. The pulp is denoted TMP.sub.HP2Fe in
FIGS. 1-3 and Tables 1-2 below.
[0040] The degree of refining, measured as the freeness value of a
pulp, is the most important parameter that influences pulp and
paper properties such as strength and light scattering ability. It
is therefore necessary to compare pulps at a constant freeness
value. Both measured and interpolated values (to freeness 100 ml
CSF) are thus provided in the text below.
[0041] FIG. 1 illustrates the freeness as a function of the
specific energy consumption (SEC) for the references (TMP.sub.Ref1
and TMP.sub.Ref2) and the pulps produced according to the invention
(TMP.sub.HP1Fe and TMP.sub.HP2Fe ). It is evident from FIG. 1 that
a substantial energy saving is obtained for the pulps produced
according to the invention whereas there was no significant
difference between the TMP.sub.Ref1 and TMP.sub.Ref2 when it comes
to energy consumption. The pulps produced according to the
invention consume 20% (TMP.sub.HP1Fe) and 25% (TMP.sub.HP2Fe ) less
energy to a constant freeness level (100 ml CSF) when compared to
the energy consumption of the references (TMP.sub.Ref1 and
TMP.sub.Ref2, see Table 2). The energy saving for TMP.sub.HP1Fe and
TMP.sub.HP2Fe was obtained with 1.0 and 1.1 wt % (on bone dry wood)
H.sub.2O.sub.2, respectively.
[0042] Moreover, it is also evident that the strength properties
(tensile and burst index, TEA) of the pulps prepared according to
the invention (TMP.sub.HP1Fe and TMP.sub.HP2Fe ) are similar to the
strength properties of the TMP references (see Tables 1 and 2).
TABLE-US-00001 TABLE 1 The pulp characteristics and energy
consumption of the produced pulps Energy Tensile Burst Freeness
comsumption index index TEA Fibre (ml CSF) (kWh/bdt) (Nm/g)
(kPam.sup.2/g) (J/m.sup.2) length.sup.1 (mm) TMP.sub.Ref1 119 2687
42.4 2.6 30.4 1.6 TMP.sub.Ref2 91 2825 54.0 3.2 54.0 1.5
TMP.sub.HP1Fe.sup.2 109 2250 44.3 2.9 34.3 1.6 TMP.sub.HP2Fe.sup.2
75 2265 54.2 3.0 46.0 1.5 .sup.1The average (length weighted) fibre
length was measured with the Kajaani FS-100 fibre size analyzer.
.sup.2Produced according to the invention.
[0043] TABLE-US-00002 TABLE 2 The pulp characteristics and energy
savings of the produced pulps interpolated to a constant freeness
value (100 ml CSF) Energy Tensile Burst Fibre saving.sup.1 index
index TEA length.sup.2 (%) (Nm/g) (kPam.sup.2/g) (J/M.sup.2) (mm)
TMP.sub.Ref1 49.5 2.7 32.3 1.6 TMP.sub.Ref2 54.3 3.2 54.0 1.6
TMP.sub.HP1Fe.sup.3 20 50.7 3.0 40.3 1.6 TMP.sub.HP2Fe.sup.3 25
51.1 2.8 42.6 1.5 .sup.1The energy saving is given relative to the
energy consumption of the TMP references (TMP.sub.Ref1 and
TMP.sub.Ref2). .sup.2The average (length weighted) fibre length was
measured with the Kajaani FS-100 fibre size analyzer.
.sup.3Produced according to the invention.
[0044] One way of reducing the energy consumption is to cut the
fibres during refining. However, one of the most important features
during production of chemimechanical or mechanical pulps like e.g.
TMP is to retain the fibre length to the greatest possible extent.
Normally, a high average fibre length gives a pulp with good
potential to produce strong papers. As seen in Tables 1 and 2, the
average fibre length of the references (TMP.sub.Ref1 and
TMP.sub.Ref2) and the pulps produced according to the invention
(TMP.sub.HP1Fe and TMP.sub.HP2Fe ) was maintained. This is further
elucidated in FIG. 2 which shows the fibre length distribution of
TMP.sub.Ref1, TMP.sub.Ref2 and selected pulps from Examples 1-3
produced according to the invention and in FIG. 3 which shows the
fibre width distribution for the same pulps measured with the
FibreMaster instrument. The freeness values of the pulps are given
in Tables 1, 3 and 5. Thus, the method according to the invention
makes it possible to produce a high-yield pulp with much lower
energy consumption without destroying the strength properties of
the pulp.
EXAMPLE 2
[0045] Black spruce (Picea mariana) thermomechanical pulp (TMP) was
debarked, chipped, preheated, and refined according to the
procedure described in Example 1 above.
[0046] A TMP reference (denoted TMP.sub.Ref1) was produced without
addition of chemicals in the same manner as was described in
Example 1.
[0047] A reference TMP produced under more acidic conditions
(denoted TMP.sub.Ref2) was produced by adding 0.19 wt % sulphuric
acid (H.sub.2SO.sub.4) based on the weight of bone dry wood to the
refiner eye (inlet) of the primary refiner in the same manner as
was described in Example 1.
[0048] A TMP produced according to the present invention using acid
hydrogen peroxide (H.sub.2O.sub.2) was produced by mixing 0.12 wt %
Na.sub.4EDTA based on the weight of bone dry wood and 0.08 wt %
iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight of
bone dry wood and then adding the mixture to the refiner eye of the
primary refiner. Hydrogen peroxide (H.sub.2O.sub.2, 1.1 wt % based
on the weight of bone dry wood) was added to the blow line of the
primary refiner. The pH of the resulting pulp was 3.7. The pulp is
denoted TMP.sub.HP1FeEDTA in FIGS. 2-4 and Tables 3-4.
[0049] The degree of refining, measured as the freeness value of
the pulp, is the most important parameter that influences pulp and
paper properties such as strength and light scattering ability. It
is therefore necessary to compare pulps at a constant freeness
value. Both measured and interpolated values (to freeness 100 ml
CSF) are thus provided in the figures and tables.
[0050] FIG. 4 illustrates freeness as a function of the specific
energy consumption (SEC) for the TMP references (TMP.sub.Ref1, and
TMP.sub.Ref2) and TMP.sub.HP1FeEDTA produced according to the
invention. TMP.sub.HP1FeEDTA consumes 19% less energy to a constant
freeness value (100 ml CSF) compared to the energy consumption of
the references TMPs (TMP.sub.Ref1, and TMP.sub.Ref2, see Table 4).
TABLE-US-00003 TABLE 3 The pulp characteristics and energy
consumption of the produced pulps Light Energy Tensile Burst Fibre
scattering Freeness consumption index index TEA length.sup.1
coefficient (ml CSF) (kWh/bdt) (Nm/g) (kPam.sup.2/g) (J/m.sup.2)
(mm) (m.sup.2/kg) TMP.sub.Ref1 119 2687 42.4 2.6 30.4 1.6 53.2
TMP.sub.Ref2 91 2825 54.0 3.2 54.0 1.5 53.1 TMP.sub.HP1FeEDTA.sup.2
118 2173 52.0 2.9 51.6 1.6 54.4 TMP.sub.HP1Fe.sup.2,3 109 2250 44.3
2.9 34.3 1.6 49.4 .sup.1The average (length weighted) fibre length
was measured with the Kajaani FS-100 fibre size analyzer.
.sup.2Produced according to the invention. .sup.3Data taken from
Table 1.
[0051] TABLE-US-00004 TABLE 4 The pulp characteristics and energy
savings of the produced pulps interpolated to a constant freeness
value (100 ml CSF) Light Energy Tensile Burst Fibre scattering
saving.sup.1 index index TEA length.sup.2 coefficient (%) (Nm/g)
(kPam.sup.2/g) (J/m.sup.2) (mm) (m.sup.2/kg) TMP.sub.Ref1 49.5 2.7
32.3 1.6 54 TMP.sub.Ref2 54.3 3.2 54.0 1.6 52
TMP.sub.HP1FeEDTA.sup.3 19 53.5 2.9 49.1 1.6 55
TMP.sub.HP1Fe.sup.3,4 20 50.7 3.0 40.3 1.6 49 .sup.1The energy
saving is given relative to the energy consumption of the TMP
references (TMP.sub.Ref1 and TMP.sub.Ref2). .sup.2The average
(length weighted) fibre length was measured with the Kajaani FS-100
fibre size analyzer. .sup.3Produced according to the invention.
.sup.4Data taken from Table 2.
[0052] The level of energy saving for TMP.sub.HP1FeEDTA is the same
as for TMP.sub.HP1Fe, i.e. about 20% when compared to the energy
consumption of the references (TMP.sub.Ref1 and TMP.sub.Ref2). In
the (TMP.sub.HP1FeEDTA experiments the strength properties (i.e.
tensile index and TEA) are, however, improved or strongly improved
compared to the TMP.sub.Ref1, and improved compared to
TMP.sub.HP1Fe (cf. Tables 3 and 4). The light scattering ability,
an important parameter for printing papers, is maintained at the
same level as for the references (TMP.sub.Ref1 and TMP.sub.Ref2).
The fibre length and width distributions were similar to those of
the TMP references (TMP.sub.Ref1 and TMP.sub.Ref2, see FIGS. 2-3).
This implies that the present invention strongly improves the
energy efficiency and strength properties of the resulting pulp
with maintained light scattering ability of the pulp.
EXAMPLE 3
[0053] Black spruce (Picea mariana) thermomechanical pulp (TMP) was
debarked, chipped, preheated, and refined according to the
procedure described in Example 1.
[0054] A reference TMP (denoted TMP.sub.Ref1) was produced without
addition of chemicals in the same manner as described in Example
1.
[0055] A TMP reference produced under more acidic conditions
(denoted TMP.sub.Ref2) was produced by adding 0.19 wt % (of bone
dry wood) sulphuric acid (H.sub.2SO.sub.4) to the refiner eye
(inlet) of the primary refiner in the same manner as described in
Example 1.
[0056] A TMP produced according to the present invention using acid
hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.08 wt %
iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight of
bone dry wood to the refiner eye of the primary refiner and 2.2 wt
% hydrogen peroxide (H.sub.2O.sub.2) based on the weight of bone
dry wood to the blow line of the primary refiner. The pH of the
resulting pulp was 3.3. The pulp is denoted TMP.sub.HP3Fe in FIG. 5
and Tables 5-6.
[0057] A TMP produced according to the present invention using acid
hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.14 wt %
iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight of
bone dry wood to the refiner eye of the primary refiner and 2.1 wt
% hydrogen peroxide (H.sub.2O.sub.2) based on the weight of bone
dry wood to the blow line of the primary refiner. The pH of the
resulting pulp was 3.2. The pulp is denoted TMP.sub.HP4Fe in FIGS.
2-3 and 5 and Tables 5-6.
[0058] The degree of refining, measured as the freeness value of a
pulp, is the most important parameter that influences pulp and
paper properties such as strength and light scattering ability. It
is therefore necessary to compare pulps at a constant freeness
value. Both measured and interpolated values (to freeness 100 ml
CSF) are thus provided in the tables below.
[0059] FIG. 5 illustrates freeness as a function of the specific
energy consumption (SEC) for TMP.sub.Ref1, TMP.sub.Ref2 and the
pulps produced according to the invention (TMP.sub.HP3Fe and
TMP.sub.HP4Fe). The pulps produced according to the described
method consume 33% (TMP.sub.HP3Fe) and 37% (TMP.sub.HP4Fe) less
energy to a constant freeness value (100 ml CSF) when compared to
the energy consumption of the references (TMP.sub.Ref1,
TMP.sub.Ref2). TABLE-US-00005 TABLE 5 The pulp characteristics and
energy consumption of the produced pulps Energy Tensile Burst Fibre
Freeness cons. index index TEA length.sup.1 (ml CSF) (kWh/bdt)
(Nm/g) (kPam.sup.2/g) (J/m.sup.2) (mm) TMP.sub.Ref1 119 2687 42.4
2.6 30.4 1.6 TMP.sub.Ref2 91 2825 54.0 3.2 54.0 1.5
TMP.sub.HP3Fe.sup.2 116 1885 47.1 2.4 40.3 1.6 TMP.sub.HP4Fe.sup.2
109 1810 47.8 2.4 41.1 1.5 .sup.1The average (length weighted)
fibre length was measured with the Kajaani FS-100 fibre size
analyzer. .sup.2Produced according to the invention.
[0060] TABLE-US-00006 TABLE 6 The pulp characteristics and energy
savings of the produced pulps interpolated to a constant freeness
value (100 ml CSF) Energy Tensile Burst Fibre saving.sup.1 index
index TEA length.sup.2 (%) (Nm/g) (kPam.sup.2/g) (J/m.sup.2) (mm)
TMP.sub.Ref1 49.5 2.7 32.3 1.6 TMP.sub.Ref2 54.3 3.2 54.0 1.6
TMP.sub.HP3Fe.sup.3 33 48.0 2.5 40.6 1.5 TMP.sub.HP4Fe.sup.3 37
49.2 2.6 41.1 1.5 .sup.1The energy saving is given relative to the
TMP references (TMP.sub.Ref1 and TMP.sub.Ref2). .sup.2The average
(length weighted) fibre length was measured with the Kajaani FS-100
fibre size analyzer. .sup.3Produced according to the invention.
[0061] It is evident from FIG. 5 that an extensive energy saving of
up to 37% (at a freeness level of 100 ml CSF) is possible to obtain
with just over 2 wt % of hydrogen peroxide according to the
procedure described in the invention. The strength properties
(tensile index, TEA) of the resulting pulps are better than or
equal to the strength properties of the TMP.sub.Ref1 (cf. Tables
5-6), and no deterioration of the fibre length and fibre width
characteristics was obtained (cf. FIGS. 2-3). The possibility to
save this amount of electrical energy without loosing the strength
properties of the resulting pulp is remarkable.
EXAMPLE 4
[0062] Norway spruce (Picea abies) wood was used for the production
of thermomechanical pulp (TMP). The wood logs were debarked and
chipped and washed prior to preheating and refining operations. A
20 inch pressurized refiner (model OVP-MEC run at 1500 rpm) was
used to produce a high-freeness pulp (about 540 ml CSF). The energy
input in the refiner was about 1150 kWh/bone dry metric ton (bdmt).
The activator and oxidant were then added to the defibrated pulp in
a mixer (Electrolux BM 10S) immediately before further refining in
a Wing refiner. The activator was first added to the pulp followed
by the addition of the oxidant. The mixing time was 30 seconds for
both activator and oxidant. The reference pulp (TMP.sub.Ref3) was
treated in the same way with the exception that deionized water was
added to the mixer to give the same pulp consistency as for the
pulp treated according to the invention. This was done since it is
well known that the pulp consistency influences the resulting pulp
properties and refining energy consumption. The pulps were then
transferred to the wing refiner for further treatment.
[0063] The wing refiner is a laboratory equipment that gives a
higher energy consumption to a fixed freeness level due to its
smaller size compared to a commercial refiner.
[0064] Each refining series described in the following examples was
produced according to the procedure described above.
[0065] A TMP reference (TMP.sub.Ref3) was produced without addition
of chemicals as described above. The degree of refining (freeness)
as a function of the specific energy consumption (SEC) can be seen
in FIG. 6.
[0066] A TMP manufactured according to the present invention using
acid hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.13
wt % copper sulfate (CuSO.sub.4.times.5 H.sub.2O) based on the
weight of bone dry wood and 2.0 wt % hydrogen peroxide
(H.sub.2O.sub.2) based on the weight of bone dry wood to the
high-freeness pulp. The pH of the resulting pulp was 3.5. The pulp
is denoted TMP.sub.HP5Cu in FIG. 6.
[0067] FIG. 6 illustrates the freeness as a function of the
specific energy consumption (SEC) for the reference (TMP.sub.Ref3)
and the pulp produced according to the invention (TMP.sub.HP5Cu).
It is evident from FIG. 6 that a substantial energy saving is
obtained for the pulp produced according to the invention.
TMP.sub.HP5Cu consume 37% less energy to a constant freeness level
(175 ml CSF) when compared to the energy consumption of the
reference pulp (TMP.sub.Ref3). The energy saving for TMP.sub.HP5Cu
was obtained with 2.0 wt % (on bone dry wood) H.sub.2O.sub.2 and
0.13 wt % (on bone dry wood) CuSO.sub.4.times.5 H.sub.2O.
[0068] The average fibre length (at 175 ml CSF, measured with the
Pulp Quality Monitor PQM 1000 instrument) was 1.7 mm for the
reference (TMP.sub.Ref3) and 1.8 mm for the pulp produced according
to the invention (TMP.sub.HP5Cu), i.e., no reduction in fibre
length occurred.
[0069] Example 4 shows that substantially energy savings is
obtained by using copper sulfate as activator and hydrogen peroxide
as oxidant according to the method described in the invention.
EXAMPLE 5
[0070] Black spruce (Picea mariana) wood was used for the
production of thermomechanical pulp (TMP). The wood logs were
debarked and chipped and washed prior to preheating (4.14 bar
steaming pressure, 40 s retention time) and refining operations. A
single disc 36'' pressurized refiner (model 36-lCP run at 1800 rpm)
was used to produce a high-freeness pulp (about 750 ml CSF). The
energy input in the refiner was about 500 kWh/bone dry metric ton
(bdmt). The activator and oxidant were then added to the defibrated
pulp in a mixer (Electrolux BM 10S) immediately before further
refining in a Wing refiner. The activator was first added to the
pulp followed by the addition of the oxidant. The mixing time was
30 seconds for both activator and oxidant. The reference pulp
(TMP.sub.Ref4) was treated in the same way with the exception that
deionized water was added to the mixer to give the same pulp
consistency as for the pulp treated according to the invention.
This was done since it is well known that the pulp consistency
influences the resulting pulp properties and refining energy
consumption. The pulps were then transferred to the wing refiner
for further treatment.
[0071] The wing refiner is a laboratory equipment that gives a
higher energy consumption to a fixed freeness level due to its
smaller size compared to a commercial refiner. It is well known
that a smaller refiner has a higher energy consumption compared to
a larger one.
[0072] Each refining series described in the following examples was
produced according to the procedure described above.
[0073] A TMP reference (TMP.sub.Ref4) was produced without addition
of chemicals as described above. The degree of refining (freeness)
as a function of the specific energy consumption (SEC) can be seen
in FIG. 7.
[0074] A TMP produced by only adding an oxidant (H.sub.2O.sub.2)
and no activator or enhancer was produced by adding 1.0 wt %
hydrogen peroxide (H.sub.2O.sub.2) based on the weight of bone dry
wood to the high-freeness pulp. The pH of the resulting pulp was
4.0. The pulp is denoted TMP.sub.HPref in FIG. 7.
[0075] A TMP manufactured according to the present invention using
acid hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.02
wt % iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight
of bone dry wood and 1.0 wt % hydrogen peroxide (H.sub.2O.sub.2)
based on the weight of bone dry wood to the high-freeness pulp. The
pH of the resulting pulp was 3.9. The pulp is denoted TMP.sub.HP6Fe
in FIG. 7.
[0076] A TMP manufactured according to the present invention using
acid hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.08
wt % iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight
of bone dry wood and 1.0 wt % hydrogen peroxide (H.sub.2O.sub.2)
based on the weight of bone dry wood to the high-freeness pulp. The
pH of the resulting pulp was 3.8. The pulp is denoted TMP.sub.HP7Fe
in FIG. 7.
[0077] A TMP manufactured according to the present invention using
acid hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.14
wt % iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight
of bone dry wood and 1.0 wt % hydrogen peroxide (H.sub.2O.sub.2)
based on the weight of bone dry wood to the high-freeness pulp. The
pH of the resulting pulp was 3.7. The pulp is denoted TMP.sub.HP8Fe
in FIG. 7.
[0078] FIG. 7 illustrates the freeness as a function of the
specific energy consumption (SEC) for the reference pulps
(TMP.sub.Ref4 and TMP.sub.HPref) and the pulps produced according
to the invention (TMP.sub.HP6Fe, TMP.sub.HP7Fe and TMP.sub.HP8Fe).
It is evident from FIG. 7 that a substantial energy saving is
obtained for the pulps produced according to the invention whereas
no energy savings is obtained when only hydrogen peroxide (oxidant)
is present (TMP.sub.HPref). The pulp produced according to the
invention consume 10% (TMP.sub.HP6Fe), 15% (TMP.sub.HP7Fe) and 33%
(TMP.sub.HP8Fe) less energy to a constant freeness level (175 ml
CSF) when compared to the energy consumption of the reference pulps
(TMP.sub.Ref4 and TMP.sub.HPref). The energy saving for
TMP.sub.HP6Fe was obtained with 1.0 wt % (on bone dry wood)
H.sub.2O.sub.2 and 0.02 wt % (on bone dry wood) FeSO.sub.4.times.7
H.sub.2O. For TMP.sub.HP7Fe and TMP.sub.HP8Fe, the corresponding
chemical additions were 1.0 wt % H.sub.2O.sub.2/0.08 wt %
FeSO.sub.4.times.7 H.sub.2O and 1.0 wt % H.sub.2O.sub.2/0,14 wt %
FeSO.sub.4.times.7 H.sub.2 O.sub.2, respectively.
[0079] The average fibre length (at 175 ml CSF, measured with the
Kajaani FS-100 fibre size analyzer) was 1.7 mm for the reference
pulp TMP.sub.Ref4 and 1.7 mm (TMP.sub.HP6Fe), 1.7 mm
(TMP.sub.HP7Fe) and 1.6 mm (TMP.sub.HP8Fe) for the pulps produced
according to the invention. The average fibre length for
TMP.sub.HPref was 1.8 mm. It is evident that no extensive fibre
shortening occurs as a result of the chemical treatment described
in this invention.
[0080] It is clear from the data presented in FIG. 7 and in the
text above that addition of an oxidant alone, such as H.sub.2
O.sub.2, is not enough to generate reduction in the refining energy
consumption. An activator must thus be added, something that the
method described in this invention stipulates.
EXAMPLE 6
[0081] Aspen (Populus tremula) wood was used for the production of
chemithermomechanical pulp (CTMP). The wood logs were debarked and
chipped and washed prior to preheating and refining operations. A
20 inch pressurized refiner (model OVP-MEC run at 1500 rpm) was
used to produce a high-freeness pulp (about 420 ml CSF). The energy
input in the refiner was about 1450 kWh/bone dry metric ton (bdmt).
The activator and oxidant were then added to the defibrated pulp in
a mixer (Electrolux BM 10S) immediately before further refining in
a Wing refiner. The activator was first added to the pulp followed
by the addition of the oxidant. The mixing time was 30 seconds for
both activator and oxidant. The reference pulp (CTMP.sub.Ref) was
treated in the same way with the exception that deionized water was
added to the mixer to give the same pulp consistency as for the
pulp treated according to the invention. This was done since it is
well known that the pulp consistency influences the resulting pulp
properties and refining energy consumption. The pulps were then
transferred to the wing refiner for further treatment.
[0082] The wing refiner is a laboratory equipment that gives a
higher energy consumption to a fixed freeness level due to its
smaller size compared to a commercial refiner. It is well known
that a smaller refiner has a higher energy consumption compared to
a larger one.
[0083] Each refining series described in the following examples was
produced according to the procedure described above.
[0084] A TMP reference (CTMP.sub.Ref) was produced without addition
of chemicals as described above. The degree of refining (freeness)
as a function of the specific energy consumption (SEC) can be seen
in FIG. 8.
[0085] A CTMP manufactured according to the present invention using
acid hydrogen peroxide (H.sub.2O.sub.2) was produced by adding 0.14
wt % iron sulfate (FeSO.sub.4.times.7 H.sub.2O) based on the weight
of bone dry wood and 2.0 wt % hydrogen peroxide (H.sub.2O.sub.2)
based on the weight of bone dry wood to the high-freeness pulp. The
pH of the resulting pulp was 3.8. The pulp is denoted CTMP.sub.HPFe
in FIG. 8.
[0086] FIG. 8 illustrates the freeness as a function of the
specific energy consumption (SEC) for the reference pulp
(CTMP.sub.Ref) and the pulp produced according to the invention
(CTMP.sub.HPFe). It is evident from FIG. 8 that a substantial
energy saving is obtained for the pulp produced according to the
invention. CTMP.sub.HPFe consume 32% less energy to a constant
freeness level (175 ml CSF) when compared to the energy consumption
of the reference pulp (CTMP.sub.Ref). The energy saving for
CTMP.sub.HPFe was obtained with 2.0 wt % (on bone dry wood)
H.sub.2O.sub.2 and 0.14 wt % (on bone dry wood) FeSO.sub.4.times.7
H.sub.2O.
[0087] The average fibre length (at 175 ml CSF, measured with the
Pulp Quality Monitor PQM 1000 instrument) was 0.95 mm for the
reference pulp (CTMP.sub.Ref) and 0.94 mm for the pulp produced
according to the invention (CTMP.sub.HPFe). It is evident that no
fibre shortening occurs as a result of the chemical treatment
described in this invention.
[0088] It is evident from the results presented in Example 6 that
the method according to the invention also generates substantial
energy savings for an aspen chemitermomechanical pulp without
cutting the fibres during refining.
FIGURE DESIGNATIONS
[0089] In the attached figures, the following units and terms are
being used:
[0090] FIGS. 1, 4-8: Freeness given in ml CSF (Canadian Standard
Freeness) on the vertical Y-axis, SEC (Specific energy consumption)
on the horizontal X-axis measured as kWh/bdt. FIGS. 2 and 3:
Proportion of the total length, 1/1000 on the vertical Y-axis,
fiber length in mm (FIG. 2); fiber width in .mu.m (FIG. 3)
respectively on the horizontal X-axis.
* * * * *